automatically set pad_to_sequence_len when use packing (axolotl-ai-cloud#2607)

* automatically set pad_to_sequence_len when use packing

* update tests

Author: winglian

src/axolotl/utils/schemas/config.py

@@ -512,10 +512,17 @@ def check_sample_packing_w_rl(cls, data):
     @model_validator(mode="before")
     @classmethod
     def hint_sample_packing_padding(cls, data):
-        if data.get("sample_packing") and not data.get("pad_to_sequence_len"):
-            LOG.warning(
-                "`pad_to_sequence_len: true` is recommended when using sample_packing"
-            )
+        if data.get("sample_packing"):
+            pad_to_sequence_len = data.get("pad_to_sequence_len")
+            if pad_to_sequence_len is False:
+                LOG.warning(
+                    "`pad_to_sequence_len: true` is recommended when using sample_packing"
+                )
+            elif pad_to_sequence_len is None:
+                LOG.info(
+                    "Setting `pad_to_sequence_len: true` to prevent memory leaks when sample_packing"
+                )
+                data["pad_to_sequence_len"] = True
         return data
 
     @model_validator(mode="before")

tests/patched/test_validation.py

@@ -648,7 +648,7 @@ def test_packing(self, minimal_cfg):
             DictDefault(
                 {
                     "sample_packing": True,
-                    "pad_to_sequence_len": None,
+                    "pad_to_sequence_len": False,
                     "flash_attention": True,
                 }
             )
@@ -662,6 +662,26 @@ def test_packing(self, minimal_cfg):
                 for record in self._caplog.records
             )
 
+    def test_packing_autoset(self, minimal_cfg):
+        cfg = (
+            DictDefault(
+                {
+                    "sample_packing": True,
+                    "pad_to_sequence_len": None,
+                    "flash_attention": True,
+                }
+            )
+            | minimal_cfg
+        )
+        with self._caplog.at_level(logging.INFO):
+            cfg = validate_config(cfg)
+            assert any(
+                "Setting `pad_to_sequence_len: true` to prevent memory leaks when sample_packing"
+                in record.message
+                for record in self._caplog.records
+            )
+            assert cfg.pad_to_sequence_len is True
+
     def test_merge_lora_no_bf16_fail(self, minimal_cfg):
         """
         This is assumed to be run on a CPU machine, so bf16 is not supported.